1. Field
The present invention relates to methods and apparatus for monitoring and controlling the properties of fluids, and more particularly to a method and apparatus for evaluating and improving the performance properties of fluid formulations, such as lubricating fluids blended with additives.
2. Description of Related Art
When developing fluid formulations, such as lubricating fluids blended with additives, analytical testing is required to ascertain that the properties of the blended lubricant are consistent with intended design properties. Lubricant formulations typically include selected additives based on the requirements of the intended application for the lubricant. All of the additives included have particular performance properties that are exploited in the final fluid formulation design. To improve the performance properties of fluid formulations, it is necessary to observe, measure and understand the combined functional effects of the additives on the physical properties of the formulation. Modifying the additives and/or the blended fluid formulation, based on observation and understanding of the additive effects, can improve both the performance and cost effectiveness of the lubricant product.
Systems for in-situ (e.g., performed in an operating system, such as an engine or transmission) monitoring the properties of lubricating fluids are known. One such system is disclosed in U.S. Pat. No. 6,278,281 entitled “Fluid Control Monitor” issued to Bauer, et al. Bauer describes a technique employing AC electro-impedance spectroscopy (referred to hereinafter as impedance spectroscopy or “IS”), and is implemented using probe electrodes that are placed in contact with a fluid under test. The method of operation includes making IS measurements at a first frequency that is less than 1 Hz and at a second frequency that is greater than 1 Hz, comparing the two IS measurements, and declaring a “pass” or “fail” condition based on a previously determined empirical relationship. This prior art lubricating fluid monitoring system disadvantageously effectively analyzes only a single property of the IS spectra based on the difference of two IS measurements. Consequently, the IS measurement technique taught by Bauer is not capable of determining the complex properties of compound fluids, as is required when designing fluid formulations having a plurality of additives.
A co-pending and commonly assigned U.S. Patent Application, application Ser. No. 10/723,624, filed Nov. 26, 2003, entitled “FLUID CONDITION MONITORING USING BROAD SPECTRUM IMPEDANCE SPECTROSCOPY,” teaches a broad spectrum IS method for determining IS parameters relating to the bulk and interfacial properties of fluids. When developing a performance-based combination of one or more additives in a base fluid, referred to herein as a “formulation,” interactions between a single additive and the base fluid, or between a plurality of additives themselves, can cause unexpected results in the performance properties of the formulation. Because the performance of the formulation depends on both the properties of both its bulk and interface, a method is needed to accurately evaluate these properties with regard to the effects of the additives, singly and in plurality. Therefore, a need exists for a method and apparatus evaluating and improving fluid formulations and additives.